Active production of new neurons and glia continues in restricted regions of the adult mammalian brain, including the subventricular zone (SVZ) lining the lateral ventricle. In these so-called neurogenic niches, neural stem cells (NSCs) and other progenitors (collectively called NPCs) persist throughout life and serve as the source of new neurons and glia. Recent studies have revealed that this continuous neurogenesis in adults contribute to physiology and pathology of the brain. Moreover, regenerating specific types of neurons after damage by manipulating endogenous NPCs is one of the important goals in restorative neurology. Yet, our understanding of the mechanisms underlying this important phenomenon is still very limited, and further research is imperative. In this proposal, we will address this issue by studying the roles for the homeodomain transcription factors Gsx1 and Gsx2 in adult neurogenesis. Gsx1 and Gsx2 control many aspects of telencephalic development, including regional specification and proliferation of NPCs, and neuronal differentiation. Their function in adults, however, has not yet been investigated. Our preliminary data show that Gsx1 and Gsx2 are expressed in specific subpopulations of NPCs that reside in anatomically discrete subdomains of the adult SVZ. We hypothesize that Gsx1 and Gsx2 play crucial roles in controlling the maintenance and/or differentiation of discrete subpopulations of NPCs in the adult SVZ, thereby contributing to the generation of specific OB interneuron subtypes. We also hypothesize that Gsx1+ and Gsx2+ progenitors contribute to injury-induced neurogenesis in the adult brain. We will test these hypotheses by experiments outlined in the following four specific aims: Aim 1: To reveal the identity of Gsx1+ and Gsx2+ progenitors in the adult SVZ. Our preliminary data show that Gsx1 and Gsx2 are expressed in NPCs that reside in discrete subdomains of the adult SVZ. We will reveal the properties of these cells by 1) detailed molecular marker analysis using Gsx2flox/+ and Gsx1::GFP mice, 2) short-term and long-term labeling with the mitotic marker 5-bromo-2'deoxyuridine (BrdU) combined with treatment with the anti-mitotic agent b-D-arabinofuranoside (Ara-C) and various growth factors, and 3) clonal cell culture assays. Aim 2: To reveal the roles for Gsx1 and Gsx2 in neurogenesis and gliogenesis in the adult SVZ. To reveal the adult-specific function of Gsx1 and Gsx2, we will perform conditional gain-of-function (GOF) and loss-of-function (LOF) analyses in vivo. Mice carrying floxed alleles of Gsx1 and Gsx2 will be used for progenitor subtype-specific knockout in the adult brain. We will also perform conditional GOF experiments using mice carrying tet-O promoter-driven Gsx1 and Gsx2 transgenes. Virus-mediated overexpression and knockdown of Gsx1 and Gsx2 will be performed in parallel. Aim 3: To reveal the function of Gsx1 and Gsx2 using in vitro culture. To better understand the mechanisms of action of Gsx1 and Gsx2, we will perform GOF and LOF analyses using clonal culture of NPCs. We will also identify the transcriptional targets for Gsx1 and Gsx2 by genome-wide chromatin-immunoprecipitation (ChIP) and transcriptome assays. Aim 4: To reveal the roles for Gsx1 and Gsx2 in injury-induced neurogenesis in the adult brain The mechanisms underlying injury-induced neurogenesis in the adult brain remain largely unknown. We will examine if Gsx1+ and Gsx2+ progenitors participate in ectopic neurogenesis following quinolinic acid (QA)-induced excitotoxic injury in the striatum. We will also determine if Gsx1 and Gsx2 play any role in injury-dependent control of SVZ progenitors and neurogenesis through GOF and LOF analyses using the aforementioned transgenic and virus-mediated approaches. Revealing the roles of Gsx1/2 in the adult brain will provide novel insights into the mechanisms for adult neurogenesis, in particular, the molecular basis for the specificity of adult NPCs. Thus, this study will significantly advance our understanding of adult neurogenesis and the biology of NPCs. Given the importance of adult neurogenesis in physiology and pathology of the brain, the outcomes of this study will have significant contribution to the promotion of human health and welfare.